The present invention relates to plastisols made from dispersions of synthetic resins in plasticizers, which contain pigments, dyestuffs, fillers, heat and light stabilizers, adhesives and other additives. These plastisols are flowable or pasty materials, which upon heating to higher temperatures will gel and after cooling form a solid, tough elastic substance.
The proportion of synthetic resin in the plastisol is formed especially by vinylchloride homopolymers or copolymers with another vinyl compound such as vinylidene chloride, vinylacetate or vinylpropionate. Acrylate polymers or acrylate copolymers also are known to be suitable.
The liquid phase of the plastisols is formed by plasticizers such as tricresylphosphate, acetyltributylcitrate, diesters of phthalic acid, adipic acid and sebacic acid with saturated and unsaturated alcohols, for instance, dioctylphthalate, diisooctylphthalate, dinonylphthalate, diallylphthalate, didecylphthalate. Other suitable plasticizers belong the the groups of the saturated and unsaturated liquid polyesters and liquid epoxide compounds. The plasticizer content in the plastisols is so chosen that it suffices to form a plastisol with a liquid to pasty consistency.
The plastisols may also contain a series of auxiliary substances and additives, for instance for controlling the viscosity, the gelling rate, the improvement in light and heat stability and storage stability, as well as pigments, dyestuffs and fillers. To improve the adhesion to the objects to be coated, the plastisols may contain known adhesion improving additives such as phenolaldehyde resins or epoxy resins with the corresponding hardener components of dicyanodiamide, amines or polyaminoamides.
The state of the art of plastisol production may be ascertained by reference to Kirk-Othmer, "Encyclopedia of Chemical Technology," Vol. 15 (1968) pages 738-740 and 771-773, and Vol. 21 (1970), pages 403-404; U.S. Pat. No. 3,050,412 and West German Published Applications Nos. 2,123,171, 2,232,885 and 2,512,366, the disclosures of which are incorporated herein.
U.S. Pat. No. 3,050,412 and the West German published applications are concerned particularly with the improvement of adhesion to metal surfaces.
Kirk-Othmer discloses in Vol. 15, pages 738-740 and pages 771-772, plasticizers used in plastisols and on pages 772-773 fillers and pigments are disclosed. Vol. 21 of Kirk-Othmer discloses at pages 403 and 404 the processing of the plastisols of polyvinylchloride and its copolymers.
Plastisols in addition to being suited to the extrusion and calendering processes also are applicable to coating by pouring, dipping and spraying methods. Textile fabrics, wood, wood materials, synthetics and metals can be used as substrates. When metals are used, the coating can be deposited directly on the untreated metal. It is advantageous however that the coating be deposited on pre-treated, phosphated, primed or lacquered metal surfaces.
As a rule, plastisol coatings require baking temperatures between 100.degree. and 250.degree. C. for the preparation of hardened films.
Plastisols are used in forming acoustically damping coatings on metals furthermore protecting against corrosion and gravel or the like, for instance, in air-conditioning ducts and on metal doors, such as automobile doors. A further very important field of application is the use as metal adhesives, for seam sealing and as undercoat protection in motor vehicles.
On technical and economical grounds, the known plastisols contain in addition to the color-imparting pigments, for instance, titanium dioxide, iron oxide pigments, cadmium pigments, also relatively high proportions of fillers such as talcum, chalk, kaolin, asbestos, silica gel, ground shale, barium sulfate, China clay, quartz and other minerals.
Because these fillers are of high densities, the specific weight of the plastisols containing the known fillers is between about 1.5 and 1.9. To obtain a good underbody or undercoat protection in motor vehicles, relatively larger layer thicknesses are required. This means, for a layer thickness of about 2-7 mm, that for a passenger car, about 20-40 kg of plastisol material is required. The relatively high weight of undercoat protective substance deposited on the vehicle as a result of the high plastisol density represents a drawback hampering the general application of plastisols in automobile construction.
Attempts have already been made to lower the density of the plastisols containing the known fillers by processing these compositions into foamed plastisols. However, this approach requires a tradeoff against the life of the coating and corrosion resistance.